I’m trying not to get all emotional about this, but… My babies are sick, they are dying!

We’ve been having tons of rain over the past few days. I went out to check on my plants yesterday and discovered that some of my tomatoes aren’t looking too good. This mostly seems to be affecting one of the varieties of tomato I’m growing, ‘Banana Legs.’

I apologize for low picture quality. This seems to affect the lower leaves first. They’re getting covered in small brown spots, and then the leaves are yellowing and wilting. Is this due to over watering, or could it be a fungus? If it’s a fungal problem, I’m trying to use ‘natural’ products if at all possible.